Myocardial perfusion and viability

Myocardial perfusion and viability assessment are important for many reasons:

• to diagnose, locate and grade the severity of coronary artery disease

• to identify candidates who would benefit from revascularization

• to evaluate response to revascularization

Terminology

Stunned myocardium

Stunned myocardium refers to a state in which there is wall dysfunction but the perfusion (resting and stress) is normal; (see the main article on stunned myocardium for more details).

Myocardial ischemia

Myocardial ischemia refers to a state in which there is decreased perfusion of the myocardium when stressed (such as during exertion) but normal perfusion during rest (seen as a reversible perfusion defect). These patients will significantly benefit from treatment.

Hibernating myocardium

With hibernating myocardium, the myocardium shows decreased perfusion on both stress and resting phase (seen as a fixed defect) but the myocytes are viable and will benefit from revascularization (see hibernating myocardium for more details).

Myocardial infarction

In myocardial infarction, there is absent perfusion both when the heart is stressed and at rest (a fixed defect) and the myocytes are not viable. There will be no benefit from revascularization; (see myocardial infarction for more details).

Imaging techniques

• thallium-201 SPECT

  • excessive radiation dose (in comparison to Tc-99m MIBI)

  • redistribution may occur

  • single injection for stress and resting phase

• technetium-99m MIBI SPECT

  • less radiation dose

  • no redistribution

  • separate injections for stress and resting phase

• FDG-PET (for viability)

  • based on the fact that the myocardium utilizes glucose for metabolism when under the effect of ischemia (hence the ischemic myocardium will show greater uptake than normal cells)

  • under normal circumstances, it utilizes fatty acids for energy

  • non-viable myocardium will not show any uptake

• cardiac MR perfusion imaging

  • no ionizing radiation exposure

  • dynamic imaging with gadolinium for perfusion

  • delayed imaging for viability assessment ³

• CT myocardial perfusion imaging

  • single phase or dynamic perfusion imaging during stress +/- rest

  • coronary arteries can be assessed at the same time